A common propulsion system for a marine craft is of the outboard type where the motor is suspended from the transom of the craft. Generally this power system is an internal combustion cylinder and piston type power plant mounted generally on a transom in a position to extend a propeller from the motor through a drive shaft connection to the power plant. A housing extends downwardly from the motor and connects the piston motor to a lower housing in which a transmission mechanism is enclosed and which directs the power from the motor to a propeller which engages the water and directs the thrust of the propeller generally horizontal to the bottom of the boat. A usual feature of the lower housing of the power plant is a horizontal extension commonly referred to as a cavitation plate. This cavitation plate functions to stabilize the craft from the forward thrust of the propeller. The stabilizing effect of the cavitation plate, along with the control of the direction of thrust by the propeller, is to a great extent dependent upon the positioning of the propeller relative to the bottom surface of the boat and therefore also relative to the mounting bracket which mounts the power plant to the boat transom.
Commonly the power plant or outboard motor is pivotally mounted on the outboard motor boat transom via a transom bracket through the use of a horizontally positioned transverse axis connection. Normally the transom brackets are of the inverted U type with one of the legs of the bracket connecting the outboard side of the transom of the marine craft while the inboard extension of the bracket extends downward along the forward or inner surface of the transom. These brackets commonly also employ some device for clamping the generally inverted U shaped bracket to the transom. The prior art apparatus generally utilized permitted the motor to be mounted on the transom in such a manner that it could be adjusted for the desired horizontal positioning of the propeller along with the cavitation plate. This adjustment was provided for so that the propeller thrust direction and the cavitation plate could be aligned relative to the bottom contour of the craft. In power boating applications, it is normally desired to have the boat "plane" in order that the maximum thrust from the propeller can be directed in the optimum direction relative to the movement of the boat. Optimum power thrust from the propeller increases the operating efficiency, economy and the speed which can be achieved from a specific combination of boat and motor.
Normally, boats employing outboard motors are loaded differently each time the boat is used. Consequently, it is not uncommon that the boat will require a different trim of the propeller for each use situation. The balance of the boat which is affected by the load, the total load of the boat and similar physical characteristics will determine the power conditions under which the boat will "plane" to thereby achieve the maximum efficiency. Further, for a given set of loading conditions, it is initially desirable to provide a maximum lift at the stern of the boat when the boat is first placed under power. Once the boat is underway, however, the maximum efficiency is achieved by adjusting the angle of thrust of the propeller as the boat approaches and achieves the planing condition relative to the surface of the water. Trimming is therefore necessary in order to achieve this maximum efficiency. Further, the proper positioning of the cavitation plate along with the propeller to achieve minimum cavitation likewise adds to the efficient operation of the boat.
Typically the mounting mechanism utilizing the U-shaped bracket is utilized for the outboard motor which provides a predetermined and limited number of fixed position stops for adjusting the trim of the motor. This is achieved by a mechanism connecting the motor to the transom bracket and the motor hanger. The fixed positional stops, while limited in number, permit some manual adjustment of the cavitation plate and propeller with respect to the hull bottom of the boat and thereby achieve greater efficiency. This type of mechanical adjustment apparatus, however, is of limited use because it provides a limited number of adjustment positions. Further, such mechanisms must be manually adjusted and normally cannot be adjusted in the presence of propeller thrust. Accordingly, the mechanism cannot be used to vary the trim of the motor when the boat is under propeller power. Consequently, the use of such an adjustment mechanism requires a compromise in the adjustment position. The compromise is between positioning the propeller for starting the boat under load and achieving some efficiency after the boat begins to plane.
In order to improve the efficiency and performance of an outboard motor boat at a variety of speeds, it is therefore necessary to provide an unlimited number of adjustments of the direction of thrust of the propeller. This unlimited adjustment capability is particularly useful for small motor boats of the type that utilize outboard motors because such small craft are dramatically influenced by the loading fore and aft. Further, the performance of these boats varies dramatically at high and low speeds with the most desired and efficient position of the boat in a planing position high in the water where the boat is not permitted to plow through the water. To be of any practical value, the mechanism used to position the propeller thrust and the attitude of the cavitation plate must be power assisted. The power assist mechanism should be convenient for operation by the boat operator while the boat is under power and should have adequate range of positioning to permit the operator to achieve maximum lift capability when the boat is started and maximum plane efficiency when the boat is under high speed operation.
A typical attempt to achieve a more efficient trimming of the motor boat propulsion system is illustrated in the following U.S. patents:
______________________________________ No. 2966876 No. 3250240 No. 3486724 No. 3053489 No. 3434450 No. 3587513 No. 3116710 No. 3473325 ______________________________________ All of the above patents disclose a power trim system which, with varying degrees of success, use a hydraulic system to adjust the trim of the boat and also to tilt the motor out of the water on occasions when the boat is at dock. All of this prior art contains the common disadvantage of utilizing a hydraulic system. The hydraulic system requires an electric power system to operate the hydraulic system which in turn provides the power to the boat trim mechanism. This hydraulic system has as a characteristic the undesirable use of fluid, tubes, reservoirs and the likelihood of leaks in that system including a significant loss of efficiency in the system.